The invention relates to a mold for the continuous casting of metal having a coolable running surface and a guide for molten metal comprising a refractory material, wherein the guide is disposed upstream of the running surface in the direction of flow. The invention also relates to a process for producing such a mold. A mold of this type is disclosed, for example, in European Patent EP 1 245 310 B1.
The mold referred to there is a hot head mold that is used for continuous vertical casting. The known hot head mold comprises a plurality of axial and concentrically disposed rings which together form the mold's flow channel. The mold's inlet opening is limited by the hot head or thermal cover, which comprises an inner ring of a refractory material and an outer ring radially encompassing the inner ring. The outer ring, on its rear end in the direction of casting, forms a flange which is joined to the mold casing. The refractory inner ring of the thermal cover is clamped axially by a clamping ring attached on the mold inlet side. To do this, the clamping ring overlaps both the inner and also the outer ring, whereby the outer ring is designed somewhat shorter in the longitudinal direction than the inner ring so that the inner ring is fixed axially to the outer ring by a suitable screwed joint of the clamping ring. Disposed downstream of the hot head in the direction of flow is a ring system which is provided for the supply of release agent and a functional ring in addition to a release agent distributor. The functional ring forms a portion of the mold's running surface, which is cooled by a cooling system.
The mold's inlet side is joined to a pouring ladle and the outlet side to a continuous casting device.
The molds generally used for continuous horizontal casting are constructed in a similar manner. Unlike the molds designed for continuous vertical casting, the molds provided for continuous horizontal casting have a nozzle plate which is disposed perpendicular to the direction of flow or strand withdrawal direction. The nozzle plate is made from a refractory material and has a nozzle aperture through which the molten metal gets into the mold. Downstream of the nozzle plate in the direction of flow or strand withdrawal direction is a running surface equipped with an oil supply, the running surface being cooled.
Particularly when starting casting, extreme temperature gradients occur in the region of the thermal cover and nozzle plate, leading to a thermally induced change in the dimensions of the nozzle plate and thermal cover. Internal stresses which may lead or actually do lead to cracks are created in the material due to thermal expansion of the nozzle plate and thermal cover. In the worst case, bleeding occurs and the mold fails.